1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus having a function of automatically detecting an original size and direction.
2. Description of the Related Art
In a conventional image forming apparatus such as a copying machine having a function of automatically detecting an original size, when an output paper size is designated to be "A4 longitudinal", for example, an enlarging or reducing magnification is automatically performed according to an original size to copy an image of the original on the output paper having the "A4 longitudinal" size. This is known as an automatic magnification selecting function. The output paper size may be designated in one of two ways, that is, (1) by selecting a paper feed cassette (tray) to thereby designate an output paper contained in the cassette, and (2) by directly designating an output paper size. However, neither of these ways can designate a plurality of output papers or cassettes.
In the case where an output paper size is designated to be the "A4 longitudinal", and an original is set in a direction corresponding to "A4 transverse" with a magnification set to 100%, a proper copy cannot be obtained. Accordingly, a copying machine having the automatic original size detecting function is generally designed to sound an alarm and call a user's attention to change a setting direction of the original or an output paper size direction. As a result, the user must change the setting direction of the original or the output paper size, so as to obtain a proper copy.
Further, in another type of copying machine having an automatic original feeding device such as an ADF, the case arises that even when the sizes of the originals are not uniform, e.g., the originals include both the A4 size and the A3 size, all the output papers of A4 size are demanded. In this case, the automatic magnification selecting function is designated, and the output paper size is selected to "A4 longitudinal", thereby obtaining a proper copy image suitably automatically enlarged or reduced to the "A4 longitudinal" size from all of the originals having different sizes. However, as shown in FIG. 2, the originals of A3 and A4 sizes must be set such that the longitudinal directions thereof are aligned to each other with respect to the ADF of the copying machine 1. Accordingly, the original having a width smaller than that of the original of the A3 size which is a maximum size tends to be obliquely taken in by the ADF because of improper operation of an original guide. Further, in the case where the ADF is so designed as to require centering of the originals, it is very hard to properly set the originals, and the user is obliged to actually classify the sizes of the originals before copying.